The invention relates to an improved apparatus and system for feeding fibers to a carding machine or the like.
Devices for feeding a web of uniform density and thickness to a card are commonly referred to as web-formers. In modern textile processing plants fibers are delivered to the web-formers, entrained in a stream of air. The air and entrained fibers are separated from one another in the web-former. For example, in U.S. Pat. No. 3,750,235, a web-former is described which uses rolls to feed fibers onto a spiked inclined apron. The fibers are transported upwardly on the spike apron which drops them down a shaft. The shaft is formed by a front wall and a shaker plate at least one of which contains a multiplicity of small perforations. The shaker plate presses the fibers introduced into the shaft thereby expressing air from the fibers through those perforations and moves the fibers downwardly to an outlet opening for feeding the fibers to subsequent textile equipment, particularly to a card.
U.S. Pat. No. 4,009,803 describes another web-former of this type with several improvements, and in which an eccentric bearing driven by a shaft which is in turn driven by a motor oscillates a shaker plate. The shaker plate divides the interior of the web-former into first and second chambers. The entrained fibers are directed by doffers into the first chamber where the air passes through perforations in the first chamber and/or a perforated height extending chamber thereabove and the fibers accumulate in the first chamber. The oscillating movement of the shaker causes the fibers to become compacted in the lower part of the first chamber, from which they are continuously removed by means of rollers or the like to form the uniform web which can then be fed to a card. A sensor is provided in at least some of the web-formers of the system for detecting the level of fibers in the first chamber. According to a prior art improvement of the system of U.S. Pat. No. 4,009,803, in at least some of the web-formers, the upper portion of the perforated plate is centrally blocked, and the doffers are eliminated so that fibers do not accumulate in the blocked upper portion of the first chamber.
One of the difficulties with the improved web-former as described above with a blocking plate is that the velocity of air passing through the perforated plate varies greatly over its surface. The velocity peaks near the blocking plate and drops by half or more towards the edge of the shaker plate. This causes problems in satisfactorily causing the fibers to be disentrained from the air and can further lead to some of the fibers blocking the perforations, rather than falling to the bottom of the first chamber.
Another difficulty is that it is desirable to entrain the fibers in the system at a high velocity. Velocities of 1400 to 1500 feet per minute are needed to keep synthetic fibers suitably moving in the middle of the conduit regardless of the size of the conduit. While natural fibers such as cotton will work at lower velocities, it is desirable to maintain sufficient flexibility in the system to be able to operate with either synthetic or natural fibers.
However, with the prior art systems described above, operation at such high velocities was not satisfactory. The fibers have a tendency at such speeds to matt at the perforated plate.
According to the present invention, the above problems are overcome in a web-former of the type having a perforated shaker plate dividing the interior of the web-former into first and second chambers by providing a passage between the conduit which carries the fibers and the first chamber, which passage increases in cross-section in the direction from the conduit to the first chamber. By increasing the cross-sectional area in the passage, the velocity of the fibers is reduced. At the same time the velocity in the conduit can be high enough to satisfactorily transport synthetic fibers. The reduced velocity fibers which enter the first chamber will satisfactorily fall to the bottom thereof and can be used to form the web. The above-mentioned problem of matting is thereby resolved.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.